(1) Field of the Invention
The present invention relates to a resin-sealed electrical device such as an IC voltage regulator, a speed warning device for an automotive vehicle or the like, which are disposed in cases and molded with resin in order to ensure water-proof tightness, resistive strength for wide temperature variations and the like.
(2) Description of Prior Art
A conventional electrical device of this kind is disposed in a case and sealed or molded with highly flexible resin such as epoxy resin, urethane resin or the like in order to protect the electrical device from the severe environmental conditions, especially from vibrations, moisture and vapor, and heating and cooling cycles. However, when the more flexible resin is arranged to be to increase its resistivity for the above-mentioned environmental conditions at lower temperature, the less resistive it becomes at higher temperature, and vi'ce ver'sa.
In order to overcome the above drawback, however, mixture of the flexible resin and granular-inorganic-insulating material has been conventionally used to seal or enclose electrical devices so that the coefficient of thermal expansion may be minimized. However, the above granular-insulating material with the resin mixed together is comparatively high in the viscosity, thus not enough to diffuse everywhere in the electrical device, resulting in another disadvantage that the electrical device can not completely be covered and sealed with the mixture.
Further, electrical devices formed on the board may be broken by wide change of temperature, since the coefficient of thermal expansion of the resin directly stuck thereon is different from that of the printed-circuit board.